1. Field of the Invention
The invention relates to a fluid delivery device, a system for feeding an exhaust gas posttreatment medium, and a motor vehicle.
2. Description of the Prior Art
Fluid delivery devices are used for the most various technical applications. In systems for feeding an exhaust gas posttreatment medium, such as a urea-water solution, into an exhaust line of an internal combustion engine, fluid delivery devices are necessary for delivering the exhaust gas posttreatment medium from an exhaust gas posttreatment medium reservoir to an injection valve for introducing the exhaust gas posttreatment medium into the exhaust line of the engine. With the exhaust gas posttreatment medium injected, pollutants in the exhaust gas of the engine are intended to be reduced in a downstream catalytic converter. The fluid delivery device pumps the exhaust gas posttreatment medium from the reservoir to the injection valve. The fluid delivery device, such as a diaphragm pump, is driven by a crank drive, for example. The fluid delivery device pumps the exhaust gas posttreatment medium to the injection valve continuously.
International patent disclosure WO 2005/024232 A1 shows a fluid delivery device of this generic type in the form of a diaphragm pump. A magnet coil is embedded in a housing. An axially movable cup-shaped piston is disposed in a bushlike slide bearing of the housing. One end of the piston is braced against a compression spring. A pump chamber is formed by an indentation of a pump head, and the pump chamber is defined on one side by a diaphragm. The diaphragm, on the side toward the piston, has an extension which penetrates a central bore in the piston. By means of two check valves, the fluid to be delivered can be introduced into and carried out of the pump chamber. When current is supplied to the magnet coil, the piston is displaced counter to the force of the compression spring until the piston rests with its flange on a set screw. In the process, the diaphragm, since it is axially solidly connected to the piston, is entrained with the piston, and as a result, the diaphragm generates an under pressure in the pump chamber. Fluid is thereby aspirated into the pump chamber. After the current supply to the magnet coil is shut off, the piston moves back by the force of the compression spring until it comes with its flange into contact with a shoulder face of the pump housing. In this axial displacement motion, the diaphragm is entrained and elastically deformed, and the fluid to be pumped that is located in the pump chamber is put under pressure, so that the fluid to be delivered is pumped out of the pump chamber by a check valve embodied as an outlet valve. The diaphragm pump is disadvantageously poorly controllable and requires the compression spring, since the magnet coil is able to generate a force in only one direction.
From German Patent DE 41 19 228 C2, a diaphragm pump of this generic type is known. A work chamber is formed by a dome-shaped pump chamber wall and by an elastic work diaphragm that is fastened in the pump housing. The work diaphragm is moved by a crank drive.